I Canīt send mails but i can receive them

Good morning everybody, Iīm trying to install a test server with ubuntu 8.04 + zimbra 6.0, before i try to replace the mail provider we are using.
After killing a lot of brain cells, I managed to install the mail server and made it work, I can ping the server from other computers, I can send & receive mails within the domain and I can receive mails from other domains, but I canīt send to them. Can some kindly soul check what is missing in my configuration files ?.
The domain names is JHERVAS.COM, the IP address es 200.51.44.146, the DNS es 200.0.243.10, the gateway is 200.51.44.145 and the name of the server is very original, MAIL.

This are my files

INTERFACES
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

// If there is a firewall between you and nameservers you want
// to talk to, you might need to uncomment the query-source
// directive below. Previous versions of BIND always asked
// questions using port 53, but BIND 8.1 and later use an unprivileged
// port by default.

// query-source address * port 53;

// If your ISP provided one or more IP addresses for stable
// nameservers, you probably want to use them as forwarders.
// Uncomment the following block, and insert the addresses replacing
// the all-0's placeholder.

forwarders {
200.51.44.145;
};

auth-nxdomain no; # conform to RFC1035
listen-on-v6 { any; };
};

-------------------------------------------
RESOLV.CONF

search jhervas.com.ar
nameserver 200.51.44.146

I have read all the DNS tutorial but the answer is still beyond me, please help me. Please excuse my english.

Well, as I mentioned earlier you hosts file is incorrect. Assuming you used the correct domain name (is this it: jhervas.com.ar) in those dig commands then you would appear to have no A ecord for your server and the MX server point to something other than the IP address you're using in your hosts file. If you have used the wrong domain name in the dig command then you appear to have an error with your DNS MX record pointing to a CNAME rather than an A record - you need to fix that and your hosts file.